The WirelessHD standard uses the 60 GHz frequency with a very high bit rate (between 3 and 6 Gb/s) and over distances of 3 to 10 meters between two transmitters/receivers in which the nature of the path of the waves between these two elements may be line of sight (LOS) or non-line of sight (NLOS), to use acronyms well known to those skilled in the art. It is then necessary to use an antenna or an antenna array whose radiation pattern in transmission and reception can be oriented and to also have a system with a significant wireless transmission gain (or “air link gain” to use a term well known to those skilled in the art).
In practice, with an antenna array (a term well known to those skilled in the art), it is possible to obtain electronic pointing in a direction by applying to the signal intended for the antennas and/or received from the antennas, different delays or phase shifts. In practice, based on the different delays or phase shifts, it is possible to adjust the direction of the radiation pattern of the antenna array.
In the state of the art, it is known practice to phase shift the signal after a double upward frequency transposition has taken place by means of mixers and two local oscillators. The phase-shifting means are then arranged downstream of the two mixers.
It is also possible to apply different phase shifts to the signal obtained from the local oscillator which is used in the second upward frequency transposition. The phase-shifting means are then connected between the second mixers and the local oscillators.
According to another alternative, the phase shifts are produced on the signal after the first transposition. The phase-shifting means are then arranged between the first mixer and the second mixer.
In all these embodiments, the phase-shifting means used are discrete, that is to say that the phase shift or phase difference between the signal at the input and at the output of the phase shifter may take a number of finite values. For example, there are phase shifters that can apply a phase shift of 22.5°, 45°, 90°, and 180°. The use of discrete phase shifters does not make it possible to address all the directions with an antenna array. On the contrary, only a few directions can be addressed.
An example of this type of antenna array is illustrated in the publication entitled, “A Thirty-two element phased-array transceiver at 60 GHz with RF-IF conversion block in 90 nm flip chip CMOS process”, by COHEN, E.; JAKOBSON, C.; RAVID, S.; RITTER, D.; in the Radio Frequency Integrated Circuit (RFIC), 2010 Congress, IEEE, pp. 457-460, dated 23 to 25 May 2010, incorporated herein by reference.
In this antenna array system, phase shifters with 4 phase-shifting levels are used, 32 antennas are used, the consumption reaches 500 mW and the size of the circuit reaches 14.5 mm2.